Those of you who read the excellent blog White Coat Underground have probably had occasion to read PalMD's explanation of the Quack Miranda Warning, the disclaimer found on various websites and advertisements that reads, "These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease." When found on a website that seems actually to be offering diagnosis, treatment, cure, or prevention, PalMD notes, this language seems like a warning that the big change that will be effected is that your wallet will be lightened.

This statement may be on every quack website but is on every legitamate website and label as well. Take vitamin C for example. Everyone knows that it can help treat & cure diseases. Vitamin C has been used for centuries to cure disease by eating various foods that are high in it. Even doctors tell you it is good to take when you are sick because it helps your body fight off the disease. So the fact that this statement is required to be on even the most obviously beneficial vitamins pretty much means that the FDA requires a companies to lie to the public and that they have failed in their one duty to encouraging truth in health. Once I realized this, it totally discredits everything the FDA says.

Sure if something is not approved by a big organization whose existance is supposed to safeguard health it makes it easier for the little con artest to step in at every opportunity, but that doesn't mean that the big con artests arn't doing the same thing

There are plenty of things that people take to be something everyone knows. (The "everyone" is tricky, because there are enough people on the planet that it's usually (always?) possible to find someone who doesn't know X.). And, I'm happy to grant that, for some values of X, there are indeed many people who believe X.

But belief is not the same as knowledge.

What "everyone knows" about celebrities should help us notice the difference. Richard Gere? Jamie Lee Curtis? Even in the event that everyone has heard the same rumors, the extent of what we actually know is that there are rumors. Our propensity to believe rumors is why the team at Snopes will never want for material.

This is not to say that we have to do all of our epistemic labor ourselves. Indeed, we frequently rely on the testimony of others to help us know more than we could all by ourselves, But, this division of labor introduces risks if we accept as authoritative the testimony of someone who is mistaken -- or who is trying to sell us snake-oil. Plus, when we're accepting the testimony of someone who knows X on the basis of someone else's testimony, our connection to the actual coming-to-know of X (through a mode other than someone else's say-so) becomes more attenuated.

At least within the realm of science, the non-testimony route to knowledge involves gathering empirical evidence under conditions that are either controlled or at least well characterized. Ideally, the effects that are observed are both repeatable in relevantly similar conditions and observable by others. Science, in its methodology, strives to ground knowledge claims in observational evidence that anyone could come to know (assuming a standard set of properly functioning sense organs). Part of how we know that we know X is that the evidence in support of X can be inspected by others. At this basic level, we don't have to take anyone else's word for X; the testimony of our senses (and the fact that others who are pointing their sense organs at the same bits of the world and seeing the same things) gives us the support for our beliefs that we need.

Claims without something like empirical support might inspire belief, but they don't pass scientific muster. To the extent that an agency like the FDA is committed to evaluating claims in a scientific framework, this means that they want to evaluate the details of the experiments used to generate the empirical data that are being counted as support for those claims. In other contexts, folks may be expecting, or settling for, other standards of evidence. In scientific contexts, including biomedical ones, scientific rules of evidence are what you get.

Why then, one might ask, might a physician suggest vitamin C to a patient with a cold if there isn't sufficient scientific evidence to say we know vitamin C cures cold?

There are a few possibilities here. One is that the physician judges (on the basis of a reasonable body of empirical evidence) that taking vitamin C is unlikely to do harm to the patient with a cold. If the physician's clinical experience is that cold patients will feel better with some intervention than with no intervention, recommending vitamin C may seem like the most benign therapeutic option.

It's also possible that some of these physicians accept the testimony of someone else who tells the there is good reason to believe that vitamin C cures colds. Being human, physicians sometimes get burned by testimony that turns out to be unreliable.

It's even possible that some physicians are not so clear on scientific rules of evidence, and that they make recommendations on the basis of beliefs that haven't been rigorously tested. The more high profile of these physicians are the kinds of folks about whom PalMD frequently blogs.

“Everyone is entitled to his own opinion, but not his own facts,” was often said by Daniel Patrick Moynihan (a riff on earlier sentiments spoken by Bernard Baruch and James Schlesinger, and probably many others).

Science is in the business of developing evidence to make facts of theories (opinions). We usually only get close to that standard but at some point in the evidence/ theory-testing process when evidence supporting the theory and no contradictions have been found, the theory moves into the "knowledge" category whence it is often used as fact.

"Why then, one might ask, might a physician suggest vitamin C to a patient with a cold if there isn't sufficient scientific evidence to say we know vitamin C cures cold?"

If the question is "why might...?", I can suggest one reason. There is a well-known placebo effect that can occur when a figure of authority prescribes some nostrum or other. In certain circumstances, it is factual that belief itself has a unique power over people.